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D. W. Burt, I. R. Paton, and B. R. Dey

ABSTRACT

The promoters for chicken transforming growth factor-β2 (TGF-β2) and TGF-β3 were cloned and sequenced to study the regulation of these genes. The promoters are GC-rich and lie within CpG islands. Several putative DNA regulatory sequence motifs were identified in the 5′-flanking regions, including matches to particular recognition sequences for several nuclear factors found in other genes. A comparison of chicken and human TGF-β2 promoters revealed a 111 bp conserved sequence surrounding the major transcription start site. Two regions of sequence homology were detected in the 5′-flanking regions of chicken and human TGF-β3 genes: an 86 bp sequence surrounding the major transcription start and a 156 bp sequence in the 5′-untranslated region. No DNA sequence homology was detected between TGF-β1, -β2 or -β3 promoters. The conserved region near the major transcription start sites in both the TGF-β2 and TGF-β3 genes, however, does show some structural homology; both promoters contain short conserved sequences that resemble TATA box, cyclic AMP-responsive element and AP-2 sequence motifs, cis-acting elements we believe may be important for promoter activity.

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B Houston, B H Thorp, and D W Burt

ABSTRACT

Longitudinal bone growth occurs in the epiphyseal growth plate and is regulated by a network of paracrine and autocrine interactions. Bone morphogenetic proteins (BMPs) are a family of growth factors whose potent osteogenic properties suggest that they may play an important role within this network, but direct evidence for this is lacking. To address this question, a cDNA encoding chick BMP-7 was cloned from a chick embryo cDNA library. Sequence homology and evolutionary arguments strongly suggested that we had cloned the chicken BMP-7 homologue. Using a reverse transcription-PCR assay, BMP-7 expression was readily detected in bone, growth plate cartilage, brain and heart, and was just detectable in liver, skeletal muscle and adipose tissue. In contrast to the pattern of BMP-7 expression in the rat and mouse, no BMP-7 expression was detected in the chick kidney. In situ hybridization was used to locate the site of BMP-7 expression more precisely within the growth plate. BMP-7 expression was confined to hypertrophic chondrocytes adjacent to and at the tips of the metaphyseal vessels. No expression was detected in the reserve zone or in proliferating chondrocytes. These results point to a specific role for BMP-7 in the growth plate, possibly in osteoblast activation or as a chemotactic agent for the metaphyseal vessels.